With the gradual reduction in Arctic sea ice extent and the continuous expansion of polar shipping routes, navigation activities in high-latitude areas have increased significantly. However, polar vessels are exposed to extremely harsh environmental conditions, with marine icing and accidental hull damage being two of the most critical threats to navigation safety. Ice accretion on ship superstructures and decks not only increases displacement but also results in non-uniform mass distribution, shifting the center of gravity upward and forward, thus significantly impairing stability. When hull damage and subsequent flooding occur under icing conditions, the combined effects can significantly increase the risk of capsizing. Existing studies have primarily focused on either marine icing or damaged stability in isolation, while systematic investigations into their coupled influence remain limited. To address this gap, this study conducts a comprehensive stability assessment of a polar vessel under combined ice accumulation and asymmetric damage conditions.

An ice accretion prediction model based on spray icing theory is first established. This model considers both wave-generated spray and wind-driven spray, which are the dominant sources of marine icing during polar navigation. The model integrates the principles of mass conservation and energy balance, considering sensible heat flux, latent heat flux, evaporative heat flux, and radiative heat flux during the entire icing process. A freezing coefficient is introduced to quantify the proportion of impinging spray droplets that freeze upon impact. The DTMB 5415 ship is selected as the reference vessel. Model validation is conducted by comparing the predicted freezing coefficient with published results, showing good agreement. Parametric analyses are subsequently conducted to investigate the effects of wind speed and ambient temperature on ice accretion over different icing durations (6 h, 12 h, and 18 h), which correspond to continuous severe weather conditions encountered by polar research vessels. Based on the predicted ice mass distribution, the variations in ship displacement, center of gravity, trim, and draft are calculated. Static stability analyses are performed for both intact and damaged conditions. The ship is subdivided into 16 watertight compartments, and an asymmetric midship damage scenario, involving Compartments No.9–No.10 on the starboard side, is considered. Righting arm (GZ) curves are calculated to assess the impacts of icing duration and hull damage on static stability, with reference to the requirements specified in the IMO International Code on Intact Stability. Furthermore, dynamic stability is assessed using the ultimate dynamic inclination angle, which represents the maximum heel angle the ship can withstand under combined wind and wave excitation. The corresponding maximum allowable wind speed is determined by analyzing the dynamic stability curve at a resonance angle of 20°, in accordance with relevant stability assessment criteria.

The results show that wind speed and ambient temperature are the primary factors influencing ice accretion. Ice accumulation increases almost linearly with wind speed due to enhanced spray production and rises rapidly as the ambient temperature decreases, with the freezing coefficient approaching unity. After 6 h, 12 h, and 18 h of icing, the total ice mass reaches 700.056 t, 1 526.124 t, and 2 213.192 t, respectively, causing a significant forward and upward shift in the ship’s center of gravity. For intact ships, increasing icing duration results in a continuous reduction in the maximum righting arm, the angle of vanishing stability, and the area under the GZ curve. The intact ship fails to satisfy the IMO static stability requirements after 18 h of icing. For damaged ships, stability deterioration is more pronounced: after 12 h of icing, the maximum righting arm decreases to 0.071 m, far below the IMO criterion of 0.2 m at a heel angle of 30°. Dynamic stability analysis further reveals the severe impact of combined icing and damage. For the intact ship without icing, the ultimate dynamic inclination angle is 64.8°, corresponding to a maximum allowable wind speed of 33.1 m/s. In contrast, for the damaged ship under 6 h of icing, the ultimate dynamic inclination angle decreases to 62.1°, and the maximum allowable wind speed drops sharply to 16.0 m/s, representing a reduction of more than 50% in wind resistance capability. These results demonstrate that the synergistic effect of ice accumulation and hull damage severely impairs both static and dynamic stability, thereby posing significant risks to polar navigation safety.

This study provides a systematic assessment framework for evaluating the stability of polar vessels under combined icing and hull damage conditions. The findings offer valuable insights for polar ship design, operational risk assessment, and the development or revision of stability criteria for vessels operating in ice-prone regions. Future work should focus on incorporating time-domain flooding processes and transient damage scenarios to further enhance the accuracy and applicability of stability evaluations for polar vessels.

Ships may encounter accidents such as collisions, groundings, and reef impacts during navigation, which can lead to hull damage and flooding, thereby significantly reducing buoyancy and stability. Under wind and wave conditions, a damaged ship's resistance to sinking is a crucial to its survivability assessment. Traditional methods evaluate the dynamic stability of ships in wind and waves by analyzing resonance angles to quantify wave effects. These methods are limited in their ability to assess the survivability and resistance to sinking of damaged ships under real-world conditions. Therefore, this study aims to develop a more comprehensive and accurate method for evaluating the dynamic stability of damaged ships under wind and wave conditions, providing a reliable reference for enhancing their survivability and safety.

Firstly, the DTMB 5415 standard ship model was selected as the test case, and its static stability parameters were calculated under typical damage conditions. Then, a single-degree-of-freedom roll motion equation for the damaged ship under the combined action of wind and waves was constructed. The CFD method was used to obtain the roll damping coefficient, which is of great significance for accurately calculating the roll motion response. Subsequently, a numerical method was employed to calculate the roll motion response of the damaged ship under wind and wave conditions. Finally, the Monte Carlo method and the Gumbel method were combined.

The results show that the proposed method takes into account the effects of wave parameters such as significant wave height and wave period on the dynamic stability of damaged ships. It was found that the wave period has a significant impact on the extreme roll motion response distribution. When the wave period approaches the natural roll period of the damaged ship, the roll motion response reaches its peak. In contrast, traditional methods based on the limiting dynamic heel angle fail to fully consider this factor. Calculations and comparisons reveal that the limiting dynamic heel angles under various wind and wave conditions are considerably greater than the extreme roll motion responses of damaged ships. This indicates that traditional methods may lead to conservative calculation results and underestimate the ability of damaged ships to withstand sudden wind-induced heeling.

The study shows that the extreme roll motion response of damaged ships under the combined action of wind and waves follows a Gumbel distribution. The Gumbel method can effectively predict this distribution. The proposed dynamic stability assessment method, which incorporates wave parameters, offers a more comprehensive evaluation than traditional methods. It is applicable not only to the dynamic stability assessment of damaged ships but also to that of intact ships, providing an important reference for ship stability assessment, which helps to improve the accuracy of ship stability evaluation and enhance the ship safety in complex sea conditions.

As global warming accelerates the melting of sea ice, the Arctic region witnesses an increase in ship navigation. The brash ice area, composed of brash ice of various sizes and shapes, is a common operational scenario for polar ships. Understanding the ice load characteristics of polar ships during oblique navigation in brash ice regions is crucial. This can enhance ship navigation safety in the complex polar marine environment, provide a reference for polar navigation route planning, and fill the gap in the current research that mainly focuses on straight-sailing conditions.

This study selects a specific type of polar ship as the research object and utilizes the discrete element method (DEM) to predict the ice loads on the ship during oblique navigation through brash ice regions. First, a numerical model of the target ship is established. The model parameters include a ship model with a scale ratio of 60, a total length of 2.04 m, a beam of 0.37 m, and a design draft of 0.13 m. The ice particles have a density of 917.0 kg/m³, a Poisson's ratio of 0.3, and other specific properties. The accuracy of the model is verified by comparing it with the experimental results from the literature under the straight-sailing condition. Then, different oblique-sailing angles (0° −15°), speeds (0.6, 0.7 m/s), and ice thicknesses (0.011 67, 0.014 97 m) are set. The ice-load calculation is carried out based on the momentum conservation equation, angular momentum conservation equation, and the linear spring contact force model in the DEM.

The results show that as the drift angle increases, the ice-breaking resistance and lateral force on the ship increase non-linearly. For example, at a speed of 0.6 m/s, an ice concentration of 70%, and an ice thickness of 0.014 97 m, when the drift angle is 15°, the ice-breaking resistance and lateral force increase by 4.25 times and 6.04 times respectively, compared to the straight-sailing condition. In terms of speed, when the drift angle is between 0° and 10°, the ice-breaking resistance increases slowly, but when it exceeds 10°, it increases significantly. The lateral force also increases non-linearly, and the influence of speed on the lateral force is more significant than whether the ship is on the ice-facing side. Regarding the influence of ice thickness, when the drift angle is greater than 10°, the ice-breaking resistance and lateral force increase significantly as the ice thickness increases.

In conclusion, this research provides reliable data support for the safety assessment of ships during oblique navigation in polar brash ice regions. It offers a valuable reference for predicting and studying ice loads on polar ships under such conditions. Ship operators should be cautious when increasing speed or entering thicker ice areas, especially when the drift angle is greater than 10°. This is to avoid potential risks caused by sudden changes in ice-breaking resistance and lateral force, ensuring the safe and stable navigation of polar ships in complex ice-covered waters.

In order to tackle the issue of the poor navigation stability of unmanned surface vehicles (USVs) under interference conditions, an intelligent control parameter adjustment strategy based on the deep reinforcement learning (DRL) method is proposed.

A dynamic model of a USV combining the line-of-sight (LOS) method and PID navigation controller is established to conduct its navigation control tasks. In view of the time-varying characteristics of PID parameters for course control under interference conditions, the DRL theory is introduced. The environmental state, action and reward functions of the intelligent agent are designed to adjust the PID parameters online. An improved deep deterministic policy gradient (DDPG) algorithm is proposed to increase the convergence speed and address the issue of the occurrence of local optima during the training process. Specifically, the original experience pool is separated into success and failure experience pools, and an adaptive sampling mechanism is designed to optimize the experience pool playback structure.

The simulation results show that the improved algorithm converges rapidly with a slightly improved average return in the later stages of training. Under interference conditions, the lateral errors and heading angle deviations of the controller based on the improved DDPG algorithm are reduced significantly. Path tracking can be maintained more steadily after fitting the desired path faster.

The improved algorithm greatly reduces the cost of training time, enhances the steady-state performance of the agent in the later stages of training and achieves more accurate path tracking.

During the anti-explosion process, the deformation and damage of blast wall connectors can lead to anti-explosion failure. Therefore, it is necessary to study the structural response characteristics of blast wall connectors under explosive loading.

Specifically, four load forms, namely triangular load, gradually applied load, linearly decaying load and rectangular load, are set in LS-DYNA in order to simulate the dynamic response of blast wall connectors under the condition that the energy of each applied load is equal.

The results show that for cases with linearly decaying and rectangular pulses, blast wall connectors are more likely to deform and suffer higher stress values. Blast wall connectors are more sensitive to gradually applied load and rectangular load, and the corresponding maximum deformation and maximum stress value can be 202.6% and 93.8% higher respectively than cases with the other two types of loads. Additionally, reverse loading conditions can lead to significant deformation, and the increment of peak pressure can induce plastic deformation under reverse pulse loads.

This study can provide useful references for the design of blast wall connectors.

A multiple unmanned surface vehicle (USV) cooperative hunting algorithm based on the double layer switching strategy is proposed to cope with the difficulties of USVs in hunting intelligent escaped targets.

Specifically, the first hunting strategy adopts the improved potential point method. The Hungarian algorithm is employed in order to dynamically allocate potential points for USVs, and the optimization goal is applied to minimize the total linear distance between USVs and potential points. In this process, the artificial potential field method is used to achieve cooperative collision avoidance. The second hunting strategy takes advantage of the nature of the Apollonius circle to tighten the surrounding area, i.e. two USVs go to the target point of the escaped target to intercept it, while the remaining USVs maintain the same direction as the escaped target. Moreover, in order to deal with the different escape strategies of targets, the first and second layers of hunting strategy can be transformed into each other.

Numerical simulation shows that the proposed algorithm can reduce the hunting time to less than or equal to that of the sequential distribution potential point algorithm and polar angle distribution potential point algorithm.

The results of this study prove the effectiveness and progressiveness of the proposed algorithm.

In this work, the influence of the initial heeling angle on the roll motion response of a ship in random beam wave is studied.

Specifically, the path integration method is applied to solve the Fokker-Planck equation, which governs the probability properties of the stochastic differential equation for the roll motion. The probability distributions of the roll motion response can then be obtained.

The results show that the initial heeling angle has limited influence on the roll motion response spectrum, but the probability density function of the roll motion response and distribution of extreme roll motion response can be significantly influenced by the heeling angle. As a result, the safety and stability of the ship will deteriorate dramatically.

The path integration method can be effective for studying the characteristics of ship roll motion under random waves.